Phosphomagnesia cements having reduced sensitivity to water

ABSTRACT

Phosphomagnesia compositions settable into improvedly water-insensitive cements that retain their mechanical properties comprise an intimate admixture of (i) a binder phase including (a) at least one phosphorous compound (P 2  O 5  or derivative/precursor thereof) and (b) at least one magnesium compound reactive therewith in the presence of water, (ii) an effective amount of cementitious aggregate, and (iii) a water sensitivity-reducing amount of at least one silicone homogeneously distributed therethrough.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present invention relates to improvedly water-insensitivephosphomagnesia cements and compositions for the formulation thereof.

2. Description of the Prior Art

One of the major applications for the phosphomagnesia cements is in therapid repair of roads, highways, bridges and airport runways. They areused to fill cracks or holes, or to cover degraded or worn areas. Otherthan adhering well to Portland cement, these phosphomagnesia cementshave a high modulus of rupture and crush resistance, which translatesthat they are particularly suitable for such applications. In addition,the setting time for these cements can be as low as a few tens ofminutes. Thus, once the route or roadway has been repaired, it can bereopened to traffic in a matter of a few hours after treatment.

The problem, however, is that the phosphomagnesia cements are sensitiveto water. Their mechanical properties deteriorate when immersed, orsimply when contacted with water.

One solution to this problem is to treat the external face surfaces ofthe cement with a waterproofing compound.

However, even though the aforesaid properties are improved, this type oftreatment is not completely satisfactory in that it is not permanent.Indeed, whatever the application of the cement, in particular thoseindicated above, they are always subject to a greater or lesser degreeof wear which causes the coating to disappear more or less rapidly. Thecement surface must then be again treated if acceptable mechanicalproperties are to be retained.

It is thus apparent that this type of solution is not satisfactory asregards the final properties of the cement, nor as regards cost, sincethe treatment must be repeated at regular intervals.

SUMMARY OF THE INVENTION

Accordingly, a major object of the present invention is the provision ofimproved formulations for the production of phosphomagnesia cementswhose sensitivity to water is considerably reduced with lasting effect.

Briefly, the present invention features the production ofphosphomagnesia cements by intimately admixing constituent elementscomprising a first, phosphorus based constituent and a second, magnesiumbased constituent, said two constituents being designated the "binder,"with at least one silicone compound and with water.

The present invention also features cement compositions, per se,comprising a first, phosphorus based constituent and a second, magnesiumbased constituent, the two constituents being designated the binderphase, and at least one silicone compound homogeneously distributedtherethrough.

DETAILED DESCRIPTION OF BEST MODE AND PREFERRED EMBODIMENTS OF THEINVENTION

More particularly according to the present invention, by the term"cement" are intended compositions comprising the aforesaid first andsecond constituents, together with, if required, the usual cementadditives, and compositions based on said two constituents indicatedabove and, optionally, conventional cement additives, and alsocomprising aggregates.

The constituent elements of the phosphomagnesia cement will first bedescribed.

The cements of this invention thus comprise a binder phase including afirst, phosphorus based constituent and a second, magnesium basedconstituent.

Any phosphorus compound can be used, provided that it includesphosphorus pentoxide, either directly or in the form of a precursorthereof.

Exemplary phosphorus based compounds include phosphorus pentoxide,phosphoric acid or derivatives thereof, such as orthophosphoric acid,pyrophosphoric acid, or polyphosphoric acid, or salts of these acids,such as the phosphates, hydrogen phosphates, orthophosphates,pyrophosphates, polyphosphates, tripolyphosphates or tetrapolyphosphatesof aluminum, calcium, potassium, magnesium or ammonium, or mixturesthereof.

It should be noted that phosphorus-containing effluents from thefertilizer manufacturing industry or from steelworks (steel pickling,corrosion reduction treatment) can be used as the phosphorus basedconstituent. Green phosphoric acid can also be used.

Salts of the phosphorus based acids indicated above are employed in oneparticular embodiment.

The phosphates and hydrogen phosphates of potassium, magnesium orammonium, or mixtures thereof, are preferably used. Ammonium dihydrogenphosphate is the most preferred.

The phosphorus based constituent can be used in either a liquid or solidform.

Preferably, said constituent is used in the solid form.

In a first embodiment, the constituent is in the form of particles, inparticular in which the granulometry is at most 300 μm. It will beappreciated that this value is not critical and that, if constituentsare used which have a particle size of more than 300 μm, grinding isdesirable prior to incorporation into the compositions of the invention.

In a second embodiment, the constituent is employed in a form which isadsorbed onto a porous support. The support may, for example, bediatomaceous earth, clay, bentonite, silica or alumina. Adsorption iscarried out via known techniques. Thus, the solution or suspension ofphosphorus based constituent is typically contacted with the support,with agitation, and the resulting suspension is heated to evaporate offthe excess liquid. This operation can also be carried out byimpregnating the support in a drum or on a rotating disc.

The second element of the binder phase comprises at least one magnesiumbased constituent.

Any magnesium compound can be used per the present invention, providedthat it reacts with the first constituent in the presence of water.

Exemplary such constituents include magnesium oxide, magnesium hydroxideand magnesium carbonate.

In a preferred embodiment, a magnesium oxide based constituent is used.Dead burned magnesia, normally obtained by calcining magnesium carbonateat temperatures in excess of 1,200° C., is particularly suitable.

The magnesium oxide can advantageously be used in its pure form, or itmay include at least one element selected from among calcium, silicon,aluminum or iron. These elements are generally in the form of the oxideor hydroxide thereof. One example of this type of compound is dolomite,a mixture containing, principally, magnesium oxide and calcium oxide.

If pure magnesium oxide is used, it is at least 80% pure.

The magnesium based constituent preferably has a specific surface areaof less than 2 m² /g. More preferably, the specific surface area is lessthan 1 m² /g.

The granulometry of this second constituent generally ranges from 10 to500 μm. Compounds having a granulometry outside this range may be used,but this presents no particular advantage. Thus, if the granulometry isin excess of 500 μm, grinding may be necessary prior to incorporationinto the composition. On the other hand, if the granulometry of theconstituents is less than 10 μm, the properties of the compositioncontacted with water may be altered. In particular, the setting rate ofthe cement may increase unless the concentration of retarding agent orretardant is increased, as will be described below. The cement producedwould then be of less importance as regards its mode of use or cost.

It should be appreciated that the two constituents described above, ifin the solid state, may be ground prior to use in the process of theinvention.

The proportion of magnesium based constituent (expressed in terms ofweight of MgO) with respect to that of the phosphorus based constituent(expressed in terms of weight of P₂ O₅) preferably ranges from 1 to 3.

The binder phase, i.e., the phosphorus and the magnesium basedconstituents, constitutes 10 to 40 parts by weight of the composition.Preferably, the binder phase constitutes 15 to 30 parts by weightthereof.

The cement prepared via the process of the invention may also comprise aretarding agent as a constituent element. More particularly, theseagents are selected from among compounds which can form a complex withmagnesium.

Exemplary such compounds include carboxylic acids such as citric, oxalicor tartaric acid, acids, esters or salts containing boron, acids, estersor salts containing phosphorus such as sodium tripolyphosphate, ferroussulfate, sodium sulfate and lignosulfonate, zinc chloride, copperacetate, sodium gluconate, the sulfate acetate of sodium cellulose, theproduct of the reaction of formaldehyde with aminolignosulfate,dialdehyde starch, N,N-dimethyloldihydroxyethylene urea,silicofluorides, tall oil and sucrose, these compounds being used eitheralone or in admixture.

Preferably, the carboxylic acids are employed, either alone or as amixture, or acids, esters or salts containing boron.

Exemplary of this latter category of compounds are boric acid and itssalts, such as alkali metal salts, for example sodium (borax), or amineor ammonium salts. Boric acid esters are also suitable, such astrialkyloxyborates or triaryloxyborates.

Preferably, the additive is incorporated in the form of a powder havingan average diameter of 10 to 200 μm.

The amount of setting retardant in the final cement ranges from 0% to 4parts by weight.

An essential parameter of the process of the invention is that at leastone silicone compound is used.

Suitable such silicones are compounds containing polysiloxane chains oftype RSiO₀.5 (unit M), R₂ SiO (unit D), R₃ SiO₁.5 (unit T) and SiO₂(unit Q). In these formulae, the radicals R, which may be identical ordifferent, may be hydrogen, linear or branched alkyl radicals, or vinyl,phenyl or 3,3,3-trifluoropropyl radicals.

More preferably, the alkyl radicals have from 1 to 8 carbon atoms.Exemplary thereof are methyl, ethyl, propyl, isopropyl, tertiobutyl,n-hexyl, or n-octyl radicals. The methyl radical is preferred.

In one preferred embodiment, a hydrogenated alkyl silicone is used.

Any hydrogenated alkyl silicone can thus be employed. Preferably, thesilicone comprises from 30 to 120 recurring structural units.

In particular, the silicone principally comprises the recurringstructural units M and D.

The aforesaid silicones may be in the form of a solution or a solid, inparticular in the form of a resin, an oil or an emulsion, preferably inwater.

The amount of silicone employed in the process of the invention ischaracteristically less than or equal to 2 parts by weight. Preferably,this amount is less than or equal to 1 part by weight.

The cements which are produced via the process of the inventioncharacteristically comprise an aggregate as a constituent elementthereof.

Exemplary of these aggregate compounds are silica, sand, alumina,zirconia, zirconium oxide, unrefined dolomite, chrome ore, limestone,clinker, vermiculite, perlite, fuel ash, or condensed silica smoke,whether used alone or in admixture.

In a preferred embodiment, sand is used which may or may not be combinedwith fuel ash and/or condensed silica smoke.

More particularly, the sand conforms to AFNOR standard NFP 15-403.

The fuel ash which can be used is typically aluminosilicate ash, inparticular from combustion in power stations.

The ash generally has a granulometry ranging from 0.5 to 200 μm.

The condensed silica smoke, which may be a constituent of thecomposition of the invention, generally has a specific surface arearanging from 20 to 30 m² /g.

The amount of aggregate advantageously ranges from 60 to 90 parts byweight. Preferably, the amount of aggregate ranges from 65 to 85 partsby weight.

Advantageously, the concentration of fuel ash and/or condensed silicasmoke in the aggregate ranges from 4 to 6 parts by weight.

The cements produced via the process of the invention can also contain,as a constituent element thereof, any known additive typicallyincorporated in cement compositions.

Exemplary such optional supplementary additives include liquefyingagents such as sodium lignosulfonate and condensates of naphthalenesulfonate, naphthalene, sodium tripolyphosphate or hexametaphosphate,ammonium hydrogen phosphate, melanin and alkyl siliconates.

Anti-foaming agents can also be employed in the process of theinvention. Exemplary thereof are the polydimethylsiloxane basedanti-foaming agents.

These additives are generally not present in amounts of more than 5parts by weight. Preferably, the amount of this additive ranges from 0to 2 parts by weight.

The process of the invention comprises intimately admixing theconstituents described above with water.

Two possible techniques may be used, namely, bringing all of theconstituent elements of the cement and water together eithersimultaneously or separately. In the latter technique, in general acomposition containing the binder phase, aggregate, retarding agent ifrequired, and all or a fraction of the optional additives describedabove is prepared. This is then mixed with water which may contain theelements not introduced into the composition in the previous step.

When the composition is pre-prepared, it will be appreciated that thesilicone employed in the process of the invention can be introduced as aconstituent of the composition, or as an additive which is introducedwith the water. The two options may be simultaneously carried out. Theessential feature is that the silicone is uniformly distributed in theresulting cement, more particularly that it is homogeneously distributedthrough the mass of the cement.

The amount of water added is such that a plastic, homogeneous andmalleable paste is obtained.

The amount of water added does not normally exceed 15% by weight, moreparticularly 10% by weight with respect to the binder phase, aggregatesand retarding agent if present.

The constituent elements of the cement are mixed together under shearingconditions, for example in a mixing machine.

The mixing operation is advantageously carried out at a temperatureclose to ambient temperature.

The mixing operation is carried out for between a few minutes and 1hour.

The setting time of the resulting cement is advantageously less than 2hours, more preferably less than 1 hour.

As indicated above, the present invention provides a composition for aphosphomagnesia cement. It comprises a first, phosphorus basedconstituent, a second, magnesium based constituent, i.e., the binderphase, and at least one silicone compound distributed therethrough.

In one preferred embodiment of the invention, such a composition has thefollowing proportions, in parts by weight:

    ______________________________________                                        (a)      Binder phase       10-40                                                      MgO/P.sub.2 O.sub.5 proportion                                                                   1 to 3                                            (b)      Aggregate          60-90                                             (c)      Retarding agent    0-4                                               (d)      Silicone           ≦2                                         (e)      Additives          0-5                                               ______________________________________                                    

In another preferred embodiment of the invention, the composition hasthe following proportions, in parts by weight:

    ______________________________________                                        (a)      Binder phase       15-30                                                      MgO/P.sub.2 O.sub.5 proportion                                                                   1 to 3                                            (b)      Aggregate          65-85                                             (c)      Retarding agent    0-4                                               (d)      Silicone           ≦1                                         (e)      Additives          0-2                                               ______________________________________                                    

The composition of the invention is formulated by mixing the elementsdefined above. Depending on the form of the various constituentelements, one skilled in this art can readily determine which order ofintroduction is most suitable, taking account that contacting thephosphorus based constituent with the magnesium based constituent in thepresence of water should be avoided, such that the reaction between thetwo constituents and subsequent solidification is not initiated.

If, for example, one or more of the elements contain water, it mayeither be dried using any known means before formulation into thecomposition, or an intermediate drying step can be carried out duringformulation of the composition such that the aforesaid two constituentsdo not come into contact simultaneously with water.

If it is preferred to formulate the above element(s) in a form whichintroduces water, then the cement proper must be used as soon as it hasbeen prepared. However, it may be more advantageous to prepare acomposition which is as complete as possible in order to simplify thefinal preparation step of the cement.

The mixing is carried out using any type of mixing machine.

The mixing operation is advantageously carried out at a temperatureranging from ambient temperature to 100° C.

This is carried out for from several minutes to 4 hours.

The composition obtained can be stored for an indefinite period of time,provided that it is not stored in the presence of water.

In order to further illustrate the present invention and the advantagesthereof, the following specific examples are given, it being understoodthat same are intended only as illustrative and in nowise limitative.

In said examples to follow, the techniques indicated hereinbelow wereused to prepare the compositions of the invention and to prepare thecement samples to provide the modulus of rupture and crush resistancevalues:

Composition preparation:

A mixture containing the phosphorus based and magnesium basedconstituents, aggregate and setting retardant was prepared andhomogenized for 1 hour between rollers.

The mixing water and additives (for example anti-foaming agent orliquefying agent), were weighed and placed in a mixing machine(conforming to AFNOR standard P15-411 (ASTM C305)) with a slow mixingspeed (60 rpm).

The mixture was rapidly poured therein and mixed slowly for 30 seconds,then rapidly (120 rpm) for 4 minutes.

Mechanical resistance/strength measurements:

Sample preparation: AFNOR standard P15-413

After mixing, the mortar was transferred into mild steel molds.

The filled mold was fixed to a compacting machine to settle the mortar.It operated as follows:

The mold was fixed to a table moved by a cam which caused a 15 mm dropshock with each turn. A period of 60 shocks was set.

After one hour, the samples were removed from the mold and dried at 21°C. in a relative humidity of 50%.

The modulus of rupture was the pressure required to break a sampleplaced in a 3-point head. An average value was taken of the threesamples prepared.

The crush resistance was determined using the broken samples (6 pieces).They were placed between two 4×4 cm jaws and compressed until theyshattered.

The result reported was the average value of the 6 pieces.

EXAMPLE 1 (Comparative)

The following composition was prepared (values given in parts byweight):

    ______________________________________                                        (i)  NH.sub.4 H.sub.2 PO.sub.4 (MAP B -                                                                 40 μm  11.5                                           RHONE-POULENC)                                                           (ii) MgO (Insulmag 4 - STEETLEY)                                                                        20 μm  13.5                                                          Specific surface area                                                         <1 m.sup.2 /g                                             (iii)                                                                              H3BO.sub.3 (PROLABO) 90 μm  1                                         (iv) Sand AFNOR NFP 15-403                                                                              --        70                                        (v)  Fuel ash             0.5-200 μm                                                                           5                                         (vi) Water                --        7.5                                       (vii)                                                                              Antifoaming agent (Rhodorsil ®                                                                 --        0.23                                           RH414 - RHONE-POULENC)                                                   ______________________________________                                    

The phosphorus based and magnesium based constituents, sand, fuel ashand retarding agent were mixed together in a mixing machine andhomogenized for about 2 hours.

The mixing water and anti-foaming agent were weighed and placed in themixing machine in contact with the mixture (AFNOR standard P 15-411).

After mixing, the resulting mixture was vibrated for 2 minutes using amechanical vibrator, then transferred into mild steel molds to provide 3mortar samples.

The samples were removed from the mold after 1 hour and dried at 21° C.in a relative humidity of 50% for 7 days.

After drying, 3 were immersed in water and 3 others were dried in airfor 7 days.

The setting time required for this formulation was 30 minutes.

The modulus of rupture and crush resistance of the samples were measuredas described.

The results obtained are reported in the following Table 1:

                  TABLE 1                                                         ______________________________________                                                      14 days   7 days dry +                                                                             Δ                                    Treatment     dry       7 days wet %                                          ______________________________________                                        Crush resistance                                                                            630       440        -30.2                                      (kg/cm.sup.2)                                                                 Modulus of rupture                                                                          120       100        -16.7                                      (kg/cm.sup.2)                                                                 ______________________________________                                    

EXAMPLE 2

Samples were prepared using the composition of Example 1, but alsoadding 1% by weight, with respect to the solids, of Rhodorsil® H68(RHONE-POULENC) hydrogenated methyl silicone oil, to the mixing water.

The modulus of rupture and crush resistance test results obtained arereported in the following Table 2:

                  TABLE 2                                                         ______________________________________                                                      14 days   7 days dry +                                                                             Δ                                    Treatment     dry       7 days wet %                                          ______________________________________                                        Crush resistance                                                                            630       590         -6.3                                      (kg/cm.sup.2)                                                                 Modulus of rupture                                                                          100       130        +30.0                                      (kg/ cm.sup.2)                                                                ______________________________________                                    

This Table 2 evidences that the addition of 1% of Rhodorsil® H68 oilretained the same dry crush resistance as the comparative sample, butgreatly improved same in a wet environment (reducing the resistance lossin both types of treatment).

When dry, even though a reduction in the modulus of rupture wasdetermined between the comparative sample and the samples containingRhodorsil® H68 oil, the addition of oil substantially improved theresistance of the material when wet (+30.0%).

While the invention has been described in terms of various preferredembodiments, the skilled artisan will appreciate that variousmodifications, substitutions, omissions, and changes may be made withoutdeparting from the spirit thereof. Accordingly, it is intended that thescope of the present invention be limited solely by the scope of thefollowing claims, including equivalents thereof.

What is claimed is:
 1. A phosphomagnesia composition of matter,comprising (1) a binder phase including (a) at least one phosphoruscompound and (b) at least one magnesium compound reactive therewith inthe presence of water, and (2) at least one hydrogenated alkyl siliconecompound homogeneously distributed in said composition of matter.
 2. Aphosphomagnesia composition of matter settable into a water-insensitivecement, comprising intimate admixture of (i) a binder phase including(a) at least one phosphorus compound and (b) at least one magnesiumcompound reactive therewith in the presence of water, (ii) acementitious aggregate, and (iii) a water sensitivity-reducing amount ofat least one hydrogenated alkyl silicone compound homogeneouslydistributed in said composition of matter.
 3. The phosphomagnesia cementcomposition as defined by claim 2, comprising a setting amount of water.4. The phosphomagnesia composition as defined by claims 1 or 2, said atleast one silicone compound comprising an organopolysiloxane.
 5. Thephosphomagnesia composition as defined by claim 4, said at least onephosphorus compound comprising phosphorus pentoxide or precursorthereof.
 6. The phosphomagnesia composition as defined by claim 5, saidat least one magnesium compound comprising magnesium oxide, magnesiumhydroxide, or magnesium carbonate.
 7. The phosphomagnesia composition asdefined by claim 5, said at least one phosphorus compound comprisingphosphoric acid, orthophosphoric acid, pyrophosphoric acid, apolyphosphoric acid, or salt thereof.
 8. The phosphomagnesia compositionas defined by claim 5, said at least one phosphorus compound comprisinga phosphate, hydrogen phosphate, orthophosphate, pyrophosphate,polyphosphate, tripolyphosphate or tetrapolyphosphate of aluminum,calcium, potassium, magnesium, or ammonium, or mixture thereof.
 9. Thephosphomagnesia composition as defined by claim 5, said at least onephosphorus compound comprising solid particulates thereof.
 10. Thephosphomagnesia composition as defined by claim 9, said solidparticulates having a granulometry of up to 300 μm.
 11. Thephosphomagnesia composition as defined by claim 5, said at least onephosphorus compound being adsorbed onto a porous support.
 12. Thephosphomagnesia composition as defined by claim 6, said at least onemagnesium compound comprising solid particulates thereof.
 13. Thephosphomagnesia composition as defined by claim 12, said solidparticulates having a granulometry ranging from 10 to 500 μm.
 14. Thephosphomagnesia composition as defined by claim 6, the ratio ofmagnesium values to phosphorus values ranging from 1 to
 3. 15. Thephosphomagnesia composition as defined by claim 2, comprising from about10 to 40 parts by weight of said binder phase.
 16. The phosphomagnesiacomposition as defined by claim 2, further comprising at least onesetting retardant.
 17. The phosphomagnesia composition as defined byclaim 16, said at least one setting retardant comprising a carboxylicacid; an acid, ester or salt containing boron; an acid, ester or saltcontaining phosphorus; ferrous sulfate; sodium sulfate orlignosulfonate; zinc chloride; copper acetate; sodium gluconate;sulfate/acetate of sodium cellulose; formaldehyde/aminolignosulfatereaction product; dialdehyde starch; N,N-dimethyloldihydroxyethyleneurea; a silicofluoride; tall oil; sucrose; or mixture thereof.
 18. Thephosphomagnesia composition as defined by claim 16, wherein said atleast one setting retardant is a powder.
 19. The phosphomagnesiacomposition as defined by claim 2, said at least one silicone compoundcomprising recurring polysiloxane structural units R₁ SiO₀.5, R₂ SiO, R₃SiO₁.5 and/or SiO₂ where the radicals R₁, R₂ and R₃, which may beidentical or different, are a hydrogen, a linear or branched alkylradical, a vinyl radical, a phenyl radical or a 3,3,3-trifluoropropylradical.
 20. The phosphomagnesia composition as defined by claim 2,comprising at most 2 parts by weight of said at least one siliconecompound.
 21. The phosphomagnesia composition as defined by claim 2,said cementitious aggregate comprising silica, alumina, zirconium oxide,dolomite, chrome ore, limestone, clinker, vermiculite, perlite, or ash.22. The phosphomagnesia composition as defined by claim 2, comprisingfrom about 60 to 90 parts by weight of said cementitious aggregate. 23.The phosphomagnesia composition as defined by claim 2, furthercomprising a liquefying agent, an anti-foaming agent, or combinationthereof.
 24. The phosphomagnesia cement composition as defined by claim3, wherein said composition is a paste.
 25. A water-insensitive hardenedcement shaped from the phosphomagnesia cement composition as defined byclaim 2.